Electromagnetic contactors are known and have been used for a long time, for example as switching means between a voltage source and an electric motor. One problem with such contactors is that one or a few of the contact pairs of a contactor may become fixed to each other by welding, and the risk of this is greater at high currents. Such welding together of contact pairs may, for example, be caused by contact bouncing when closing the contactor towards a high making current of an electric motor.
The fact that one or more contact pairs become fixed by welding may entail serious harmful effects. Upon an opening signal to a contactor with a welded-together contact pair, the armature will move a certain distance in the opening direction, because of the resilience in the mechanical coupling, and then stop in an intermediate position. This may cause arcs in the contact pairs which are not welded together, and fire, explosion or other damage to the contactor and other equipment. In many applications, it may also, and independently thereof, cause serious consequences that a contactor does not open when, according to a supplied opening signal, it should have opened.